https://jsommers.github.io/cbook/cbook.pdf
Might be a good way for someone who is familiar with a higher level language.
Than there is of course "The C Programming Language" by Ritchie and Kernighan and "advanced programming in the unix enviroment" by stevens and rago.
So, i'd guess just get your feet wet with small stuff. Find out how to take arguments from the command line, or read a file, maybe programm a simple guess the number game. After you are more familiar with the syntax and so on you could look into using your c code in a higher level language. For python you'd have to look into ctypes for that.
Harvard’s CS50 course is free online and does a pretty good job touching on the fundamentals of C in the first half.
Ever since edX had their IPO, I hesitate to call it free. Each edX course is free for a limited time now and their prices are way too high if you aren't interested in a certificate and the certificates aren't worth much of anything in the employment market. They need a $50 option for no certificate and "unlimited" course access. But with shareholders, would they ever consider such a thing?
The content isn’t exclusive to edX, though.
Harvard hosts it outside of edX.
That puts a bit of organizational overhead on the learner. The material is all there and organized, but it's not as conveniently presented nor does it mark your progress automatically. I like that they switched to GitHub code spaces and away from cloud9 which complicated things further.
Programming
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